The present invention relates generally to variable air volume systems for maintaining a desired temperature range within buildings and, more particularly, to an improved controller for enabling the required air volume to be supplied.
In variable air volume systems for cooling the interiors of buildings, the cooling coils are maintained at a substantially constant temperature by a continuously operating compressor while a controller establishes the volume of air forced through the cooling coils and distributed throughout the building to maintain a desired temperature range. This controller is connected to operate a speed changing means which results in fan speed changes to vary the volume of air. The inputs to the controller are means sensing temperature of the areas of the building being cooled and a feedback indicative of the speed of the fan.
In some prior variable air volume systems, a heat cycle is provided before the cooling is introduced. In some systems, direct current drives the fans, some have eddy current drive means, while others use two speed motors with variable inlet vanes. The alternating current fan drive and controller of this invention operate with a significantly shorter payback period than the above alternatives. This invention further contributes considerable amounts of energy saved. Since the power consumed is a function of the cube of the fan speed, the variable speed provides fan operation at speeds substantially below maximum a considerable part of the operating time. The initial cost is low; and the maintenance requirements, efficiency at partial loads, overload capacity, complexity of controls, and the requirements of maintenance training are favorable to the structure of this invention.
In the prior art, the variable pitch split pulley transmission system was utilized in cooling of engines such as is shown in U.S. Pat. No. 3,872,842 issued Mar. 25. 1975 to Jackson C. Medley. In the application of such speed changing mechanism to air conditioning systems, as in the present invention, unique control circuitry is contributed.